Slow Boat or normal

[Private Nemo]

Hi, I have a 1985 Formula 28pc with twin Merc 260's. Last weekend was my first time out with the boat. Enjoy it very much. But, I was disappointed with the speed of the boat. At full throttle I was running at 3500 rpms and 34 mph.

Does that sound right , I thought it was a little slow.

Drew

 

[Bob_VT]

Re: Slow Boat or normal

yup too slow......

Your motors do not sound like they are reaching their peak and optimum rpms. You should be seeing 4400-4800 rpms at WOT

You have some troubleshooting to do.

 

[Private Nemo]

Re: Slow Boat or normal

Engines seem to run perfect. New carbs and complete tune up. I am leaning towards wrong props. Anybody have any idea what would be the best props for this boat ?

Drew

 

[cr2k]

Re: Slow Boat or normal

Ones that will will run at max RPM at WOT with boat loaded as usually used.

 

[spoilsofwar]

Re: Slow Boat or normal

Engines seem to run perfect. New carbs and complete tune up. I am leaning towards wrong props. Anybody have any idea what would be the best props for this boat ?

Drew

What is the pitch of the props you have on now?

 

[Augoose]

Re: Slow Boat or normal

From another article....

Think of a propeller as you would a car's axle ratio. The lower the ratio, the more pulling power from a standstill. The same is true with a prop. The lower the pitch, the better your hole-shot. However, this comes at a price: top speed.The lower pitch makes the engine reach maximum rpm at slower speeds.

Conversely, a higher pitch will deliver greater top speeds, but slower acceleration. Be aware that lower-horsepower engines can bog down if fitted with a propeller with too high a pitch and diameter, and that can wear heavily on internal engine parts.

If you're changing pitch on a recreational boat, remember that each inch of pitch is worth about 200 rpm.Lowering the pitch will increase rpm and vice versa. For example, going from a 23 pitch to a 21 pitch will increase engine rpm by about 400 revolutions.

 

[Private Nemo]

Re: Slow Boat or normal

Hi , Thanks for the replys. This is my first season with the boat, so I am working out the bugs. It came with stainless steel props, I assume they were right for the boat, oops. I have know idea what size they are , didnt check
. So now I am trying to find out what was the original prop on this boat , not an easy task.